Embodiments of the present disclosure generally relate to magnetic resonance imaging (MRI) systems.
MRI is a medical imaging modality that generates images of the inside of a human body without using x-rays or other ionizing radiation. MRI or Nuclear Magnetic Resonance (NMR) imaging generally provides for the spatial discrimination of resonant interactions between Radio Frequency (RF) waves and nuclei in a magnetic field. Typically, an MRI system includes a superconducting magnet that generates a main magnetic field within an imaging volume. The MM system uses various types of radio frequency (RF) coils to create pulses of RF energy. The RF coils transmit RF excitation signals and receive magnetic resonance (MR) signals that the MRI system processes to form the images.
A body resonator or birdcage configured to be disposed around a patient may be employed to transmit RF waves to generate a RF field. Conventionally, the birdcage may include two conductive rings disposed at opposite axial ends, with the two conductive rings joined by conductive rungs extending between the rings. (For an example of such a birdcage, see U.S. Pat. No. 4,692,705). The resonator or birdcage may be connected to a power amplifier, which sends energy to the resonator to be transformed into an RF field. The power may be sent through the resonator via 2 channels, for example via a quadrature splitter. For instance, an RF amp may transmit 32 kiloWatts (kW) of power through a first channel of 16 kW and a second channel of 16 kW, with the two channels at a phase difference of 90 degrees, with the RF field circularly polarized. However, with power sent through two channels for the entire resonator, there is limited adjustability for making the RF field more uniform, for example. Also, adjustment of power provided via the channels to form a field as desired may be slow and/or inaccurate due to limits on the detection of power. For example, even if power is accurately detected, the current in any given rung (or each of the rungs) may still not be accurately determined due to system losses.